1. Field of the Invention
The present invention relates to a refreshing apparatus for a dynamic type memory, such as a dynamic random access memory (DRAM), which requires a refreshing control in order to hold data stored in dynamic storage cells.
2. Description of the Related Art
In general, dynamic type memories are comprised of memory cells arranged with MOS transistors. MOS transistor implemented memory cells are operated dynamically, and random access memories comprised of such memory cells are known as a "DRAM". A refreshing operation is required, in a predetermined time interval, for holding data stored in such memory cells of the DRAM.
Very recently, the memory integration capacity for DRAM is becoming higher and higher, i.e., 256 Kbits, 1 Mbits, 4 Mbits and 16 Mbits. Accordingly, utilization of such a higher-memory-capacity DRAM is expanded. For instance, there are handheld type compact electronic appliances employing the higher-memory-capacity DRAM, e.g., an electronic notebook capable of storing and displaying names and telephone numbers; an electronic scheduler capable of storing and displaying dates, times and schedules; and an electronic time table capable of storing and displaying departure times for a bus, a train and an airplane. Moreover, the higher-memory-capacity DRAM may be utilized in a voice recording/reproducing apparatus for recording/reproducing the voice information supplied externally by coding/decoding this voice information.
In the above-described compact electronic appliances employing such a higher-memory-capacity DRAM, the refreshing operation is continuously required for not only the data writing operation into DRAM and the data reading operation from DRAM, but also the data storage. This causes high power consumption in DRAM. More specifically, since these compact handy type electronic appliances are portable and thus a small-sized battery is employed as a power source, the power consumption is continuously effected by performing the refreshing operation even when the operation of the compact electronic appliances is interrupted, resulting in shortening the battery life. As a consequence, such a small-sized battery must be frequently replaced with a new battery.